CX/Gravel Tire Test: Silca Protocol RCR 38

Silca is an American (with Italian heritage) cycling parts and accessories brand known for its high-quality products. Over the past few years, we've seen them become more interested in the tire market; they started carrying tubeless sealant, tapes, and valves, and introduced their TPU tubes late last year. They recently entered the tire market head-on; alongside their gravel bike tire release, they also launched the Protocol RCR, a full-slick tire available in 29, 34, and 38 mm.

A couple of weeks ago, we published our review of the 29 mm version of the Protocol RCR, and today we're testing the largest size available: the 38 mm version. Silca claims the Protocol RCR's architecture is volume-centric, starting with the 38 mm size and then scaling that design down to 34 and 29 mm. From that perspective, this review will be even more interesting than our initial test of the 29 mm size.

When we revisit the specifications, we notice that the 38 mm size is much more competitive when we compare its specified weight with the competition. While the 29 mm size has a specified weight of 290 grams, the jump to 38 mm adds only 60 grams, making it instantly more competitive, since we usually see a weight increase of around 100 grams for that size increase.

This time we're going to compare the 38 mm Silca Protocol RCR to a range of 35 and 38 mm full-slick road bike tires and a couple of 40 mm semi-slick gravel bike tires. We've done all the tests, and you can find our test results and conclusion below. If you need a bit more introduction to the Protocol RCR range and want to compare it to the hottest 28/29 mm road bike tires, we suggest jumping over to our review of the 29 mm size.

Manufacturer Specifications

Manufacturer Specs
Brand	Silca
Model	Protocol RCR
Year	2026
Supplied By	Bought in store
New or Used	New
Mileage	0 km
Price Range	Very High
Buy At
Manufacturer part number	-
EAN	810093163397
TPI	120
Compound	Pulsar Compound
Bead	Folding
ETRTO	38-622
Specified Weight	354 grams
Max Air Pressure (psi)	58
Made In	Pro Data
Available Sizes	29-622 (700x29c) 34-622 (700x34c) 38-622 (700x38c)

Silca Protocol RCR 38 Test Results

Size, Weight, and Thickness Measurements

Size, Weight, and Thickness Measurements
Specified Weight	354 grams
Measured Weight	354 grams
Measured Width Casing	35 mm (un-round)
Measured Width Tread	33 mm
Measured Height	Pro Data
Tire Circumference	Pro Data
Measured Knob Height Center	0.0 mm
Measured Knob Height Edge	0.0 mm
Measured Total Thickness Center (excluding knobs)	2.10 mm
Measured Total Thickness Sidewall	Pro Data
All size measurements are taken at low air pressure on a 17.8 mm inner width rim.

Rolling Resistance Test Results

Rolling Resistance Test Results
Inner Tube	None (30 ml sealant)
Measured Width	35 mm
Rolling Resistance Real tire width in mm: 30-32 = 66 psi/4.6 bar 33-35 = 60 psi/4.1 bar 36-38 = 54 psi/3.7 bar 39-42 = 50 psi/3.4 bar 43-46 = 46 psi/3.2 bar 47-50 = 42 psi/2.9 barHigh Air Pressure (60 psi / 4.1 bar)	Pro Data
Rolling Resistance Real tire width in mm: 30-32 = 55 psi/3.8 bar 33-35 = 50 psi/3.4 bar 36-38 = 45 psi/3.1 bar 39-42 = 42 psi/2.9 bar 43-46 = 38 psi/2.6 bar 47-50 = 35 psi/2.4 barMedium Air Pressure (50 psi / 3.4 bar)	Pro Data
Rolling Resistance Real tire width in mm: 30-32 = 44 psi/3.0 bar 33-35 = 40 psi/2.8 bar 36-38 = 36 psi/2.6 bar 39-42 = 33 psi/2.3 bar 43-46 = 31 psi/2.1 bar 47-50 = 28 psi/1.9 barLow Air Pressure (40 psi / 2.8 bar)	15.6 Watts CRR: 0.00468
Rolling Resistance Real tire width in mm: 30-32 = 33 psi/2.3 bar 33-35 = 30 psi/2.1 bar 36-38 = 27 psi/1.9 bar 39-42 = 25 psi/1.7 bar 43-46 = 23 psi/1.6 bar 47-50 = 21 psi/1.4 barExtra Low Air Pressure (30 psi / 2.1 bar)	Pro Data
The CX/Gravel section is a multi tire size section, air pressures have been adjusted to the measured casing width. All numbers are for a single tire at a speed of 29 km/h / 18 mph and a load of 42.5 kg / 94 lbs. Use the formula: RR (Watts) = CRR * speed (m/s) * load (N) to calculate rolling resistance at a given speed and load.

Puncture Resistance Test Results

Puncture Resistance Test Results (higher is better)
Total Puncture Score Tread	40 Points
Total Puncture Score Sidewall	Pro Data
Tread Puncture Force Sharp Needle	Pro Data
Tread Puncture Force Blunt Needle	Pro Data
Tread Total Tire Thickness	2.10 mm
Sidewall Puncture Force Sharp Needle	Pro Data
Sidewall Puncture Force Blunt Needle	Pro Data
Sidewall Total Tire Thickness	Pro Data

Hard Surface Static Grip Test Results

Static Grip Test Results
Wet Grip Average	85 Points
Wet Grip Center	Pro Data
Wet Grip Edge	Pro Data
Measured Knob Height Center	0.0 mm
Measured Knob Height Edge	0.0 mm
Grip in points = coefficient of friction * 100 CX/Gravel grip test rim width = 23.0 mm
Wet Grip Test and Off-Road Tires (info)

Conclusion

The 38 mm Silca Protocol RCR isn't the fastest-rolling 35/38/40 mm full-slick tire, but it delivers strong all-round performance, with its strongest point being wet grip and low weight. Compared to the competition in a similar size, the 38 mm Protocol RCR is more competitive than the 29 mm size, and we attribute that to its lower relative weight. Road bike competition is fierce, and designing a tire for a particular size can make the difference and help gain those last few points of performance.

The 38 mm Protocol RCR is a bit small, measuring just 34.5 mm wide on our 18 mm internal test rim. The 35 mm Grand Prix 5000 S TR measures 34.5 mm on the same rim, making it easy to compare. The Grand Prix 5000 S TR remains the strongest choice for rolling resistance, but the Protocol RCR outperforms it in wet-grip tests and sidewall strength.

Other interesting competitors are the 35 mm Pirelli P Zero Race TLR RS and Michelin Pro 5 TLR, both a bit narrower at ~33 mm wide but rolling a bit faster than the Silca. The Silca is lighter and has stronger sidewalls, but the Pirelli matches or beats it in every other test. The Michelin comes close to the Pirelli but costs much less and is also available in the even bigger 40 mm size.

• Protocol RCR 38 and Grand Prix 5000 S TR 35
• Protocol RCR 38 and P Zero Race TLR RS 35
• Protocol RCR 38 and Michelin Pro 5 TLR 35

RATING: 4.8 / 5
TEST VERDICT: Highly Recommended

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